1. Field of the Invention
The present invention relates to a light-emitting device. In particular, the invention relates to a light-emitting device using an organic EL element.
2. Description of the Related Art
Organic EL (Electro Luminescence) elements have been actively researched and developed. The basic structure of the organic EL element is as follows: a layer containing a light-emitting organic compound is interposed between a pair of electrodes; and light emission can be obtained from the light-emitting organic compound when voltage is applied to the element.
The light-emitting device using an organic EL element is, for example; a lighting device, or an image display device including a thin film transistor. The organic EL element can be formed in a film shape and thus easily increased in area, which allows a lighting device with a planar light source to be realized. In addition, an image display device using an organic EL element needs no backlight which is necessary for liquid crystal display devices and the like; therefore, thin, lightweight, high contrast, and low power consumption display devices can be obtained.
It is known that when the organic EL element is exposed to the air (including moisture, oxygen, and the like), its performance degrades rapidly. It is thus required that the organic EL element be hermitically sealed with a material having a high gas barrier property so as not to be exposed to the air.
A sealing technique using glass frit including low-melting-point glass is known as a technique that realizes sealing with a high gas barrier property. The technique disclosed in Patent Document 1 is as follows: a paste containing a binder and a frit material including low-melting-point glass is applied to the edge of a glass substrate; the binder is removed through prebaking; and the glass frit is irradiated with laser light while a counter glass substrate is provided over the glass substrate, whereby the glass frit is melted and the substrates are bonded to each other and sealed with the glass frit. When a device using an organic EL element is sealed with such glass frit, the organic EL element can be isolated from the external air and a light-emitting device with high reliability can be realized.